### Function

# GLib HashFunc

#### Declaration

    guint
    (* GHashFunc) (
      gconstpointer key
    )

#### Description [src]

Specifies the type of the hash function which is passed to `g_hash_table_new()` when a `GHashTable` is created.

The function is passed a key and should return a #guint hash value. The functions g_direct_hash(), `g_int_hash()` and `g_str_hash()` provide hash functions which can be used when the key is a #gpointer, #gint, and #gchar respectively.

`g_direct_hash()` is also the appropriate hash function for keys of the form `GINT_TO_POINTER (n)` (or similar macros).

A good hash functions should produce hash values that are evenly distributed over a fairly large range. The modulus is taken with the hash table size (a prime number) to find the ‘bucket’ to place each key into. The function should also be very fast, since it is called for each key lookup.

Note that the hash functions provided by GLib have these qualities, but are not particularly robust against manufactured keys that cause hash collisions. Therefore, you should consider choosing a more secure hash function when using a GHashTable with keys that originate in untrusted data (such as HTTP requests). Using `g_str_hash()` in that situation might make your application vulnerable to Algorithmic Complexity Attacks.

The key to choosing a good hash is unpredictability. Even cryptographic hashes are very easy to find collisions for when the remainder is taken modulo a somewhat predictable prime number. There must be an element of randomness that an attacker is unable to guess.

#### Parameters

`key`

  Type: `gconstpointer`

  A key.

  The argument can be `NULL`.
  The data is owned by the caller of the function.

#### Return value

Type: `guint`

The hash value corresponding to the key.